1. Technical Field
The present invention relates to a sealing structure, an interference filter, an optical module, and an electronic apparatus.
2. Related Art
There is a known spectroscopic filter of related art that causes light to be reflected off and between a pair of reflection mirrors in such a way that light of a specific wavelength according to the distance between the reflection mirrors is acquired out of incident light whereas light that does not have the specific wavelength is eliminated in a destructive interference process. As a spectroscopic filter of this type, there is a known interference filter of wavelength tunable type (wavelength tunable interference filter) configured to be capable of adjusting the distance between the reflection mirrors to select the wavelength of light to be acquired (see JP-A-2005-309174, for example).
In general, a wavelength tunable interference filter is sensitive to moisture, foreign matter, and other environmental factors, which may degrade or otherwise affect a driver that changes the dimension between the mirrors and the mirrors themselves and hence degrade drive and optical characteristics of the interference filter, possibly resulting in a decrease in reliability thereof.
In contrast, the wavelength tunable interference filter described in JP-A-2005-309174 includes a first substrate on which a fixed reflection surface is formed, a second substrate which is so bonded to the first substrate that the second substrate faces the first substrate and on which a movable reflection surface is formed, and a glass substrate provided on the opposite side of the second substrate to the first substrate and bonded to the second substrate via a spacer. A sealed internal space is created between the first substrate and the second substrate, and another sealed internal space is created between the second substrate and the glass substrate.
In JP-A-2005-309174, since the first substrate and the second substrate are so bonded to each other that the internal space therebetween is sealed, usable bonding methods are limited. For example, direct bonding, anode bonding, surface activated bonding, and other bonding methods generally usable for hermetical sealing tend to be greatly sensitive to flatness of bonding surfaces and other conditions thereof. That is, the bonding surfaces need to be smooth, otherwise sufficient bonding strength will not be achieved.
On the other hand, bonding based on a plasma polymerization film or a resin is unlikely to be sensitive to the flatness of bonding surfaces and can hence achieve sufficient bonding strength but has a difficulty in maintaining sealing performance.
As described above, when a pair of substrates are so bonded to each other that the space created between the substrates is sealed and protected against the atmosphere, it is difficult to achieve both satisfactory bonding strength and sealing performance. In an interference filter, in particular, when the first substrate and the second substrate are bonded to each other, it is necessary to control the thickness of a bonding layer because the distance between the mirrors needs to be equal to a design value. In this case, usable bonding methods are limited. It is therefore further difficult to achieve both satisfactory bonding strength and sealing performance.